Batteries that last 20 years ? (Single-Crystal NMC532/AG)

We wrote about how to double the life of your expensive lithium battery packs back in March of 2017 (for that story, click here). This was based on experimental results by Jeff Dahn, who is now the head of Tesla’s battery research department. Well, he’s at it again, and over the last two years, he is now claiming that they have unlocked the methods that can allow lithium battery packs last over 8,000 cycles, which is 20 years of normal EV use.

Our previous article on extending battery life highlighted how there are simple things that an ebike owners could do to make their lithium battery pack last much longer, up to twice as long (regardless of how you use your battery pack). They are:

A) Charge to 4.1V per cell, instead of the standard 4.2V (and 4.0V is even slightly better).

It seems like every week there is some new PR announcement about some fantastic new battery chemistry that will quadruple battery pack range, or make them dirt cheap. This has been going on for years, and yet we still haven’t seen these developments result in a REAL battery pack that can be independently tested by a third party, to verify their claims.

Whenever I see these announcements, I look to see who is making them. If it is from Panasonic, Samsung, or Tesla…I actually read the article. If it is from some hot new start-up who is “looking for investors”, I just don’t have enough spare time to waste on all of them. However…this announcement is by Jeff Dahn from Tesla.

Although Tesla cars remain fairly expensive (I approve of this. Wealthy early adopters are financing the advancement of EV tech, which is the way it should be). However, the major complaints from the people who were likely to NEVER buy a Tesla are that the range will be too short, the performance will be just adequate, and the expensive battery pack will need to be replaced too often.

Each iteration of the available Tesla models has gotten less expensive. First the Roadster, then the Model-S, and now thousands of customers are driving the Model-3. As far as performance, they all perform extremely well, and the Model-S with the P100D option is defeating so many so-called “supercars”, that few want to publicly compete with them, out of sheer embarrassment. Millionaires who have dozens of gasoline-powered supercars are buying the P100D, based on performance alone (click here)…Aaaand also click here.

As far as the expensive pack dying too often and needing to be replaced, Tesla understood this deep-seated concern of their customers, and took the bold move of providing an 8-year warranty on their packs (meaning, after eight years of daily use, it would retain at least 80% of the new-pack range). However, instead of just sitting on these impressive laurels, they have been expending extensive resources to develop the next generation of better battery packs.

If you read about how chemical batteries work, most people immediately look for any other elements that may have better characteristics as far as energy density. An element with twice the potential energy density could possibly result in batteries with twice the range, or…the same range at half the size of today’s battery packs.

In fact, lithium was identified many decades ago as a potentially useful base-material for batteries, but…pure metallic lithium is highly reactive and unstable. It was only after experimentation proved that making an ion of lithium was safe enough, and had acceptable performance, that our modern batteries began their rapid journey to the packs we have today.

Silicon, Sodium, and Sulfur are all frequently mentioned as possible future materials for battery packs. An often mentioned feature is that these are all abundant and cheap (along with having a potentially high energy density). I have been told by an engineer in the battery field that the cost of the base materials are a tiny fraction of the total cost of the actual cells. The vast majority of the costs are the processes to make and assemble the anode, cathode, separators, and electrolyte in a way that works.

Think of it like a common chunk of wood. It’s so cheap that it’s almost free, but after a master craftsman carves it into a sculpture or some type of clever mechanism, the final cost is MUCH more than the cost of the wood. So…the benefit of someday figuring out how to make a useful battery with any one of these three is focused on making sure that no vital battery-production material can be restricted by international trade disputes or wars, along with moving towards batteries that are not made of hazardous material when they are at the end of their life-cycles.

That being said, this new scientific paper describes a variation of the Lithium-NMC chemistry (Nickel-Manganese-Cobalt). Tesla has been using Lithium-NCA (Nickel-Cobalt-Aluminum) in their cars, and NMC in their home installations, called the “Tesla Powerwall”. The NCA chemistry had a minor benefit for raw performance, but…at lower amp-draws like their powerwall, the NMC chemistry had a minor benefit for life-cycle longevity.

LFP and LTO?

Lithium-Iron-Phosphate (LiFePO4) was known years ago as a chemistry that could last over 1,000 full cycles (2-3 times better than common NCA/NMC found in the popular18650-format cells). However, it’s nominal voltage (the average between full and empty) is 3.2V, sooo…it takes more of these cells to equal the same voltage of the common 18650 cells that use NCA/NMC, meaning a bigger battery for less range.

LTO (Lithium Titanate Oxide) is not common. It is known for being able to charge and discharge at a high rate, and also for lasting for a useful life that is often quoted as over 7,000 full cycles. However, it’s nominal voltage is even lower than LFP, at only 2.4V per cell.

Using a solid electrolyte will make batteries extremely fire-safe, but the big news is that SSB’s will dramatically reduce the battery pack volume, while maintaining the same energy density. This can almost double the range of existing battery packs of a given size, but…I suspect almost all of them will use the SSB tech to shrink the packs (while maintaining the same range), so the packs will be smaller, lighter, and perhaps cost less…

_________________________________________________

532…Whut?

The “532 ” number means that the added Nickel, Manganese, and Cobalt in this lithium-Ion battery chemistry is:

0.5% Nickel

0.3% Manganese

0.2% Cobalt

This also explains why it “used to be” called NCM, and now it is NMC. Tesla has steadily reduced the amount of cobalt per weight in their battery packs, since cobalt was identified early on as a restrictive limitation on how many batteries they could build. The order of the letters is based on their percentage in the formula…

I also suspect that [based on previous efforts] they will soon announce an aggressive program to recycle the cobalt in Tesla battery packs that have reached the end of their lives…

__________________________________________________

Dendrites and Cathode Build-up

The SEI is the Solid Electrolyte Interphase layer. As you cycle a lithium battery hundreds of times, the SEI is the build-up resulting from a chemical reaction on the Cathode that slowly degrades the range of the cell. It’s like a small hole at the bottom of a car’s gasoline tank that slowly gets bigger over time. It’s mentioned in the previous paper from Jeff Dahn that we referenced earlier, and it’s also mentioned in this new paper he published.

“Dendrites” are a type of buildup that has a spikey shape, and over time they can puncture the plastic separators inside the cell and cause a short, which then causes a sudden and rapid death-spiral that ends in a fire.

_________________________________________________

What does this new paper ACTUALLY say?

Here are a few copy/paste quotes to condense the main points of this long and detailed paper.

“…Up to three years of testing has been completed…Tests include long-term charge-discharge cycling at 20, 40 and 55°C [ed. 68, 104, 131F]…Several different electrolytes are considered in this Li-Ni0.5-Mn0.3-Co0.2-O2/graphite chemistry, including those that can promote fast charging…the average daily driving range for…gasoline vehicles in the US was 32.6 miles (52 km) and that the vast majority of daily range need is in the 0–50 mile range (0 – 80 km). For an EV with a 400 km range this represents about 25% DOD on a daily basis [ed. Depth of Discharge]…

...taxis or long haul trucking…Electric buses represent another application where duty cycles approaching 100% DOD are used on a daily basis…

...testing results on Li-Ni0.5-Mn0.3-Co0.2-O2/Artificial Graphite (NMC532/AG) cells are presented. The NMC532 used in these cells is “single crystal” NMC532 as described in the papers [links provided] The artificial graphite (AG) used in these cells is provided by Kaijin (China) and is grade AML-400…

...some testing results are given for lower DOD ranges such as…3.0V to 4.1V, to show the advantages…The NMC532 used in these cells was single crystal NMC532 as described by Li et al. with a Ti-based coating [ed. Titanium] as described by [link provided]…

...the cycling of these cells is incredibly impressive between 3.0 and 4.1 V with no measurable loss in 3C capacity [ex. 3C = a 10-Ah cell can provide 30-Amps]…A cell…was tested for 5300 cycles at 20°C using currents corresponding to 1C. The voltage limits were 3.0 to 4.1 V. The cell had 97% of its initial capacity remaining…

...Figure 22 shows representative cross sectional SEM images of the electrode particles after 5300 cycles. No evidence of micro-cracking can be observed in particles that were initially less than 3 micrometers in size, demonstrating again the advantages of single crystal materials…

[ed. the high-definition SEM images of the crystals is the picture at the header of this article]

...Most important to realize is that Figure 23 assumes 100% DOD cycling on every cycle and storage at full state of charge…10 years of lifetime to 70% capacity and a total driven distance of 1,200,000 km is projected [ed. 745,000 miles]. It is worth noting that only 3650 cycles would be required for this total driven distance and 3700 cycles have been demonstrated in Figure 16…

Here’s what I got from this paper…

This paper is the opposite of all the other vapor-ware PR announcements I see every week. They are usually looking for “investment partners”. Jeff Dahn works for Tesla, and is fully funded….they don’t want your investment money.

Next, there are always big claims to get readers excited, and to gain a lot of “buzz” headlines, but…the details are always “secret until we get the global patents locked down”. This paper spells out ALL the details so that the cell-design and chemistry can be replicated and verified by independent third parties.

And as far as patents go, as mentioned above, Tesla has been patenting promising tech to make sure nobody else will lock them away, and then they make the patents available to everyone [See: Texaco Cobasys, click here]…

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas

1 Comments

( September 10, 2019 )

You write, “A) Charge to 4.1V per cell, instead of the standard 4.2V (and 4.0V is even slightly better).” for a longer lasting battery. Our 48-volt. 20 AH battery is now in its 20th month of almost daily use and recharging. Not long ago, smart me managed to cause a momentary short at the RCA-female charge port that required replacing the RCA-female connector. To prevent repeating this boo-boo I added a 1N5408 diode (1,000 volts / 3 amps) in series between the RCA charge port and the battery, anode to charge port and cathode to battery, so energy can go into the battery but cannot come out of the battery at the charge port. Don’t know if this will extend the life of the battery or not as our normal 2-amp charger still lights up green and shuts down when the battery is charged.